1. Field of the Invention
This invention relates to a hydrodynamic gas foil bearing assembly having conical rotor elements. The bearing assembly is useful in turbochargers for internal combustion engines. The bearing assembly may also be used in other turbine applications such as small aircraft engines.
2. Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine's cylinders via the engine's intake manifold.
The turbine wheel and the shaft of a turbocharger rotate very fast. The rotation speed of a turbocharger shaft depends upon the size of the compressor and turbine wheels. The maximum wheel speeds for aluminum compressor wheels, titanium compressor wheels, and inconel turbine wheels are 560 m/s, 600 m/s, and 530 m/s, respectively. Therefore, smaller wheels render higher maximum turbocharger rotating speed. The turbine wheel operates in a high temperature environment and may reach temperatures as high as 1922° F. (1050° C.). This heat is conducted to the turbocharger shaft and the bearing housing. The rapid rotation of the turbine shaft creates frictional forces which further heat the bearing area. Accordingly, turbochargers have a need for a low friction bearing assembly, and a flow of fluid for cooling.
In practice, foil bearing supported turbomachinery fails, at extreme operating conditions (high temperature and high rotating shaft speeds), due to poor thermal management. In particular, thermoelastic distortion of the thrust runner due to heat transfer within the bearing system results in deformations larger than the gas film thickness, which causes system failure. Thrust foil gas bearings have lower load capacity at extreme operation conditions because of difficulty in thermal management.
U.S. Pat. No. 8,189,291 relates to a fluid dynamic bearing (FDB) system for use within a hard-disk drive. A fluid dynamic bearing system may comprise an upper conical bearing and a lower conical bearing that are both disposed along a stationary shaft on which a magnetic-recording disk is rotatably mounted. The upper conical bearing and the lower conical bearing may have different cone angles, diameters, and/or lubricants to produce a desired difference in stiffness between the first conical bearing and the second conical bearing. By adjusting characteristics of the fluid dynamic bearing system to achieve the desired bearing stiffness ratio, the tendency for the magnetic-recording disks to experience a sustained vibration when the hard-disk drive receives a mechanical shock is reduced. By preventing the magnetic-recording disks from sustained vibration after a mechanical shock, data may be written to and read from the magnetic-recording disks with greater reliability.
U.S. Pat. No. 8,181,462 relates to a single-shaft exhaust gas-driven turbocharger that includes two parallel-flow first-stage centrifugal compressors in series with a single second-stage centrifugal compressor, and a one-stage turbine arranged to drive both the first- and second-stage centrifugal compressors via a single shaft on which the compressors and turbine are fixedly mounted. The compressor housing defines from one to a plurality of circumferentially spaced inlet ducts for the second wheel of the first stage, and from one to a plurality of circumferentially spaced interstage ducts leading from a vaneless diffuser of the first stage into the inlet of the second stage. In accordance with one embodiment, a first bearing assembly rotatably supports the shaft at a location between the turbine and the second-stage centrifugal compressor, and a second bearing assembly rotatably supports the shaft at a location between the first-stage centrifugal compressors and the second-stage centrifugal compressor. Advantageously, the first bearing assembly includes ball bearings and can comprise, for example, two axially spaced ball bearings. The second bearing assembly advantageously comprises a foil air bearing.
U.S. Pat. No. 7,988,426 relates to a compressor ported shroud that takes compressed air from the shroud of the compressor before it is completely compressed and delivers it to foil bearings. The compressed air has a lower pressure and temperature than compressed outlet air. The lower temperature of the air means that less air needs to be bled off from the compressor to cool the foil bearings. This increases the overall system efficiency due to the reduced mass flow requirements of the lower temperature air. By taking the air at a lower pressure, less work is lost compressing the bearing cooling air.
U.S. Pat. No. 7,553,086 relates to a journal foil bearing comprising a retaining member having an inner surface which defines a shaft opening within which a rotatable shaft is receivable for rotation; and a foil assembly affixed to and lining the inner surface and comprising a plurality of foil sub-assemblies each subtending a circumferential segment, of the inner surface. Each of the foil sub-assemblies may comprise an under foil sandwiched between a spring foil disposed radially outwardly of the under foil, and a top foil disposed radially inwardly of the under foil, the under foil, the top foil, and the spring foil each having a leading edge distal from a trailing edge in a direction of rotation of the rotatable shaft, and each of the under foil, the top foil, and the spring foil being affixed to the retaining member along their respective leading edge, their respective trailing edge, or both their respective leading edge and their respective trailing edge, wherein a radius of curvature of the top foil is less than a radius of curvature of the under foil. A method of supporting a rotating shaft is also disclosed.
U.S. Pat. No. 7,108,488 relates to a turbocharger that includes a foil bearing assembly mounted in a center housing between a compressor and a turbine of the turbocharger. The bearing assembly forms a unit installable into the center housing from one end thereof, and the center housing is a one-piece construction. The bearing assembly includes a foil thrust bearing assembly disposed between two foil journal bearings. The journals foils are mounted in annular bearing carriers fixedly mounted in the center housing. A radially inner portion of a thrust disk of the thrust bearing assembly is captured between a shaft and a shaft sleeve of the turbocharger. The center housing defines cooling air passages for supplying cooling air to the foil bearings, and optionally includes a water jacket for circulating engine coolant through the center housing.
U.S. Pat. No. 5,498,083 relates to a method and apparatus for increasing the load capacity and damping capability of a three pad compliant foil gas bearing by establishing a gas pressure force between each pad and a shaft supported by a sleeve containing the bearings.